1. Field of the Invention
The invention relates to an acceleration change detection system, which in a preferred embodiment is used as an impact detection system. More particularly, the invention relates to such a system that employs a deflection sensor. The invention may have particular use in a system that determines whether to deploy an air bag in a vehicle.
2. State of the Art
Detection of movement and forces has wide application. For example, automobile air bag systems employ accelerometers in determining whether to inflate the air bag.
Prior art detectors used in deploying air bags have included a cylinder in which a ball is ordinarily held in place by a magnet at one end of the cylinder. A spring is positioned at the other end of cylinder. The cylinder and the ball are gold plated to be electrically conductive. When the vehicle has a collision at the front, the vehicle including the cylinder rapidly decelerates. When there is sufficient force, the ball breaks loose from the magnet and travels toward the spring. Accordingly, the magnet is chosen to have enough magnetic force to hold the ball in place unless a threshold force is created through a collision. The threshold force varies depending on vehicle specifications.
When the ball strikes the spring, an electrical circuit is completed, causing a squib switch to be activated and in turn causing an explosion which inflates an air bag.
Disadvantages of the prior art detection system include that it detects an impact in only one direction and generally lacks flexibility of application.
Accordingly, there is a need for an impact detection system that will detect impact in various directions and has flexibility in applications.
An acceleration change detection system includes a deflection sensor having an electrical parameter that changes upon deflection of the deflection sensor. The deflection sensor may be a flexible potentiometer. The deflection sensor may be deflected against a deflection structure. The deflection structure may include any of a variety of shapes. A non-pivoting attachment may also facilitate deflection. The system may include a movement inhibitor that ordinarily prevents the deflection sensor from deflecting within a particular range of deflection, but that allows deflection within the particular range in response to sufficient change in acceleration of the movement inhibitor. Examples of a movement inhibitor include magnets, springs, and clips. A particularly stiff substrate of the deflection sensor may also inhibit movement.
Determining circuitry that is connected to the deflection sensor may generate a signal indicative of a value of the electrical parameter and determine whether the deflection sensor is deflecting within the particular range based on the indicative signal. The determining circuitry may respond to merely the presence of deflection, that the deflection exceeds a threshold, or to a particular value of a threshold. In each case, the deflection is within a range. The system may include air bag triggering circuitry for triggering an air bag.
The system may include more than one deflection sensor, each having an electrical parameter that changes upon deflection of the deflection sensor for detecting deflections in various directions. The deflection sensors may be joined in a group (for example, to a chassis and/or in a loop) or separated. The determining circuitry may generate signals indicative of values of electrical parameters of the additional deflection sensors, and determines whether the deflection sensors are deflecting within particular ranges based on the indicative signals. Vector mathematics may be used to determine a direction.
Deflection values may be stored for forensic purposes.